In these latter days, electronic apparatuses have been introduced for controlling in various electrical equipment in a vehicle such as an automobile. As an example of the electrical equipment in which an electronic apparatus is incorporated, an electric power steering apparatus is provided with a motor driving unit in an enclosure accommodating an electric motor for steering of the automobile. The electronic apparatus is installed in the motor driving unit. The electronic apparatus is incorporated as the power module in the motor driving unit.
The power module is constituted as a so-called semiconductor module on which a power element such as a field effect transistor (FET) or insulated gate bipolar transistor (IGBT), for example, suitable for controlling an electrical equipment such as the electric power steering apparatus driven by relatively high current. This kind of power module is also called “In-vehicle Module” since it is installed in a vehicle.
As this kind of semiconductor module, a semiconductor module illustrated in FIG. 14 has been known conventionally, for example (see Patent Document 1). FIG. 14 is a cross-sectional schematic view of an example of a conventional semiconductor module.
The semiconductor module 100 illustrated in FIG. 14 is provided with: a substrate 101 made of metal; a resin 102 provided on a bottom flat surface of a recess portion of the substrate 101; and a plurality of copper foils (wiring patterns) 103a, 103b, 103c, and 103d formed on the resin 102. Grooves 109 are formed between the copper foil 103a and the copper foil 103d and between the copper foil 103c and the copper foil 103d. Then, thermal buffer plates 104a and 104b are formed on the copper foils 103a and 103b out of the plurality of copper foils 103a, 103b, 103c, and 103d, respectively. IGBTs 105a and 105b are formed on the buffer plates 104a and 104b, respectively. Each of the IGBTs 105a and 105b is a bare-chip IGBT (bare-chip transistor).
Then, the emitter of the IGBT 105a and the copper foil 103b are jointed to each other by a wiring 106a constituted of a wire, and the emitter of the IGBT 105b and the copper foil 103c are similarly jointed to each other by a wiring 106b constituted of a wire.
Additionally, the resin 102, the copper foils 103a, 103b, and 103c, the buffer plates 104a and 104b, the IGBTs 105a and 105b, and the wirings 106a and 106b are sealed by a gel 107. Additionally, a cover 108 for covering the recess portion of the substrate 101 is fixed at an upper portion of the substrate 101.
As another example of a conventional semiconductor module, a semiconductor module illustrated in FIG. 15 has been also known, for example (see Patent Document 2). FIG. 15 is a plane schematic view of another example of the conventional semiconductor module.
The semiconductor module 200 illustrated in FIG. 15 is provided with a plurality of conductive pads 201 and 202 formed on a substrate (not illustrated). Then, a MOS chip 203 is connected by soldering on one conductive pad 201 out of the plurality of conductive pads 201 and 202. Additionally, a plurality of source electrodes 205 and a single gate electrode 204 are formed on the top surface of the MOS chip 203, and a drain electrode, not illustrated, is formed on the lower surface of the MOS chip 203.
Then, the source electrodes 205 of the MOS chip 203 and another conductive pad 202 out of the plurality of conductive pads 201 and 202 are jointed with each other by a lead 210. The lead 210 is formed by punching and bending a metal plate, and is provided with: a rectangular tabular source electrode jointing portion 211 extending in the X direction and Y direction (horizontal direction) illustrated in FIG. 15; a tabular electrode jointing portion 212 extending in the X direction and Y direction; and a coupling portion 213 coupling the source electrode jointing portion 211 with the electrode jointing portion 212 and tilting in the Z direction (up-down direction). In this situation, the source electrode jointing portion 211 is jointed by soldering with the source electrodes 205 of the MOS chip 203, and the electrode jointing portion 212 is jointed by soldering with the another conductive pad 202 out of the plurality of conductive pads 201 and 202.
The width “a” of the source electrode jointing portion 211 in the X direction is equal to or longer than the width “b” of the plurality of source electrodes 205 in the X direction. This makes it possible to prevent non-uniform solder wetting on the source electrodes 205 and displacement of the source electrodes 205 due to the reflow of the solder.